The present invention relates to a laser device which is edge emitting and comprises two or more laser structures in one and the same optical cavity. Devices of this kind can e.g. be used in various light transmission systems such as in fiber optical transmission systems etc. For most diode lasers the threshold current, i.e. the lowest electrical feeding current for which lasering occurs is high whereas the electrical feeding impedance is low. That diode lasers normally has very low electrical input impedances among others makes the construction of broadband feeding circuits under maintenance of a high efficiency difficult.
A number of different laser devices with two or more active regions are known. Examples thereof are e.g. so called strip lasers. The reason for them having several active regions is however to increase the power intensity. The active regions therein are furthermore not electrically connected in series.
From for example U.S. Pat. No. 4,602,370 a laser device is known which has several active layers in a large optical cavity. The different active layers are arranged vertically with intermediate so called distance layers. These active layers are not electrically connected in series and the optical losses are high.
In "Intergrated multilayers GaAs lasers separated by tunnel junctions" by J P van der Thiel and W T Tsang, Applied Physics Letter 41 (6), 15 Sep., 1982 three so called double heterostructure GaAs-laserdiodes are connected in series through reversed tunnel junctions. Also in this device the active layers are arranged vertically but the arrangement does not form a vertical optical cavity. Since the active layers in such a device are arranged on a relatively large distance from each other, which as such is necessary in this case to avoid optical losses in the contact surfaces or in the tunnel junctions, the different optical light signals from the different lasers will be incoherent since the lasers are not connected to each other.
As mentioned above, in well known devices such as for example diodelasers, the electrical input impedance is very low and the threshold current for lasering is high. This has as a consequence considerable difficulties with the construction of broadband feeding circuits where it is desireable that the efficiency also is high. At the same time impedance adaption through various transmission wires or others gets difficult or impossible.
With known devices the dynamic impedance is as low as a few ohms, often only a fraction of one ohm which is very hard to adapt to for example 50 .OMEGA. due to the large reflection.
In applicant's copending U.S. patent application "Surface emitting laser device with a vertical cavity" application Ser. No. 08/303,623, filed Sep. 9, 1994, a device is described through which a low treshold current and a high impedance is obtained wherein further the resistive, electrical losses which are introduced through the electrical reflection devices, are reduced. Applicant's copending U.S. patent application "Optical amplifying device", application Ser. No. 08/303,621, filed Sep. 9, 1994 an amplifying device is described which uses laser structures or active regions connected in series for example in a longitudinal optical cavity according to the present invention or a vertical optical cavity in accordance with the abovementioned application. Both of these copending U.S. patent applications are incorporated by reference in this application.